Sawai made his debut in Weekly Shōnen Jump drawing one shotmanga such as Mutekiman and Fierce!! Rock Paper Scissors Island!!, all of which have a gag aspect of manga, usually using satire and visual gags. Not too long after beginning to work for Shōnen Jump, Sawai began experimenting with various concepts regarding characters who fought with bizarre bodily functions, including a hero who fought with farts and a poop-headed hero. His most successful experiment was a Fist of the North Star parody involving a strange afro-haired man who fought against "Hair Hunters" using his nose hairs in a post-apocalyptic society. The character, as well as the story itself, was Bobobo-bo Bo-bobo. Over several one-shots, Sawai further defined Bo-bobo as well as introducing other characters, including damsel-in-distress Beauty, fellow nosehair fighter Gunkan, rival fart-fighter Heppokomaru, and a strange star-shaped creature and fellow "Hajikelist" known as Don Patch. After the success of these one-shots, Bo-bobo became a weekly series in 2001, where it had a long and successful run until its conclusion in 2007. Sawai's art style is a mix of very blocky-looking characters and, sometimes, very detailed art. He tends to focus on the realistic appearance of his characters' facial expressions when they freak out. Because of the nature of his series, he has often written Bo-bobo version parodies of other authors' manga, including Akira Toriyama's Dragon Ball, Yudetamago's Kinnikuman, Kazuki Takahashi's Yu-Gi-Oh!, and Tsugumi Ohba's and Takeshi Obata's Death Note. He was also the leader of a team of gag-based manga artists who wrote a special 30th anniversary chapter of Osamu Akimoto's Kochira Katsushika-ku Kameari Kōen-mae Hashutsujo. Sawai returned to the magazine in September 2008 with new series Chagecha. He has also published a children's storybook, Kirarinchoshirizu. In December 2011 Sawai started a spin-off manga of Don Patch from Bobobo-bo Bo-bobo entitled Fuwari! Don Pacchi in Saikyō Jump. A sequel to the spinoff titled "Honnori! Don Patch" was serialized in the Shonen Jump+ app until its conclusion in August 2015.
